1. Field of the Invention
The present invention relates to an ink jet recording head, an ink jet recording apparatus using such ink jet recording head, and a method for manufacturing ink jet recording head.
2. Related Background Art
Of recording methods for a printer or the like, the ink jet recording method for forming characters, images, and the like on a recording medium by discharging ink for discharge ports (nozzles) has been widely adopted recent years, because it is non-impact recording method having a lesser amount of noises, while it can perform recording operation in high density at high speed.
A general ink jet recording apparatus is provided with an ink jet recording head; means for driving a carriage that mounts it; means for conveying a recording medium, and means for controlling them. The ink jet recording apparatus thus structured, that performs recording operation with the carriage, which is made to travel, is called serial type. On the other hand, the one that performs recording operation only by conveying a recording medium without the traveling of an ink jet head, is called line type. For the ink jet recording apparatus of line type, many numbers of nozzles are arranged in line all over the widthwise direction of a recording medium.
The ink jet recording head is provided with energy generating means for generating the discharge energy, which is given to ink in the nozzle in order to discharge ink droplets from the nozzle. As means for generating energy, there is the one that uses electromechanical converting element, such as piezoelectric element, the one that uses electrothermal converting element, such as heat generating resistive member, or the one that uses electromagnetic wave mechanical converting element or electromagnetic wave heat converting element, which converts electric waves of radio wave, laser, or the like into mechanical vibrations or heat, among some others. Of these methods, the type that discharges ink droplets by the utilization of thermal energy makes it possible to perform recording in high resolution, because nozzles can be arranged in high density. Particularly, the ink jet recording head that uses electrothermal converting element as the energy-generating element is easier to make it smaller than the head using electromechanical converting element. Further, such head has an advantage that it can fully utilize the IC technologies and micro machining techniques, the advancement and reliability of which have made a remarkable progress in the field of semiconductor manufacture in recent years, for easier assembling in high density at lower costs of manufacture.
As the ink supply method for an ink jet recording head, there is the one, which is of the so-called head-tank integrated type where the ink tank containing ink and the ink jet recording head are made one body; the one, which is of the so-called tube supply type where an ink tank and an ink jet recording head are connected by use of tube, or the one, which is of the so-called pit-in type where an ink tank and an ink jet recording head are provided separately, and the ink jet recording head moves to the position of the ink tank as required to connect them, and ink is supplied during such operation.
If the capacity of an ink tank is made larger in order to make the frequency of ink tank replacements smaller, the weight of the ink tank should increase. Therefore, in consideration of the increased weight given to the carriage of an ink jet recording apparatus of serial type then, it is not preferable to adopt the head-tank integrated one. Consequently, the ink jet recording apparatus of serial type that uses an ink tank of larger capacity adopts the tube-supply type or pit-in type more often. Of such types, the tube supply type, which makes it possible to perform a continuous recording for a long time, is adopted more often, because the pit-in type needs to suspend recording operation during the period of ink supply.
Hereunder, with reference to FIG. 16, the description will be made of the ink supply system of an ink jet recording apparatus of tube supply type.
The ink supply system shown in FIG. 16 is provided with a main tank 1204 containing ink 1209 therein; a supply unit 1205 detachably installed in the main tank 1204; and a recording head 1201 connected with the supply unit 1205 through a supply tube 1206.
The supply unit 1205 has an ink chamber 1205c therein. The ink chamber 1205c is open to the air outside by way of an atmosphere communication port 1205g, while it is connected with the supply tube 1206 at the bottom thereof. Also, for the supply unit 1205, there are fixed the ink supply needle 1205a and the air induction needle 1205b, the lower ends of which are positioned in the ink chamber 1205c, and the upper end of which are extruded from the upper face of the supply unit 1205, respectively.
The lower end of the ink supply needle 1205a is positioned lower than the lower end of the air induction needle 1205b. 
The main tank 1204 has two connector portions formed by rubber plug or the like at the bottom thereof in order to close the inside of the main tank 1204 airtightly. Thus, the main tank is structured to be airtight individually. When the main tank 1204 is installed on the supply unit 1205, the ink supply needle 1205a and the air induction needle 1205b penetrate the connector portions, respectively, so as to enter the inside the main tank 1204. Now that the positions of the lower end of the ink supply needle 1205a and the air induction needle 1205b are defined as described above, ink in the main tank 1204 is supplied to the ink chamber 1205c through the ink supply needle 1205a, and the air outside is inducted into the main tank 1204 through the air induction needle 1205b so as to compensate for the reduction of pressure in the main tank 1204. When ink is supplied into the ink chamber 1205c up to the position where the lower end of the air induction needle 1205a is immersed in ink, the ink supply from the main tank 1204 to the ink chamber 1205c is suspended.
The recording head 1201 is provided with a sub-tank portion 1201b in which a designated amount of ink is retained; an ink discharge portion 1201g where a plurality of nozzles is arranged for discharging ink; and a flow path that connects the sub-tank portion 1201b and ink discharge portion 1201g. For the ink discharge portion 1201g, nozzles are arranged with the opening surface thereof being placed downward, thus discharging ink downward. In each nozzle of the ink discharge portion 1201g, the aforesaid energy generating means is arranged. The sub-tank portion 1201b is positioned above the ink discharge portion 1201g, and the supply tube 1206 is connected with the sub-tank portion 1201b. Between the sub-tank portion 1201b and the flow path 1201f, a filter 1201c is installed with a fine mesh structure for preventing the nozzle from being clogged by minute foreign substances in ink that may otherwise enter the ink discharge portion 1201g. 
The area of the filter 1201c is defined to be a value to make the pressure loss by ink to be less than the allowable value. The higher the pressure loss of the filter 1201c, the finer is the mesh of the filter 1201c, and also, the more is the flow rate of ink passing the filter 1201c. On the contrary, the pressure loss is inversely proportional to the area of the filter 1201c. There is a tendency that the pressure loss becomes higher in a micro-dot recording head having many nozzles at higher-speed recording in recent years. Therefore, the area of the filter 1201c is made as large as possible in order to suppress the increase of pressure loss.
The nozzle is opened to the atmosphere, and also, the opening surface of the nozzle is placed downward. Therefore, in order to prevent ink leakage from the nozzle, it is necessary to keep the inside of the recording head 1201 to be negatively pressurized. On the other hand, if the negative pressure is too great, the air enters the nozzle to disable the ink discharge from the nozzle eventually. Here, therefore, in order to enable the inside of the recording head 1201 to be negatively pressurized appropriately, the recording head 1201 is arranged so that the position of the nozzle-opening surface becomes higher by a height H than the liquid surface of ink in the ink chamber 1205c, thus keeping the inner condition of the recording head 1201 at negative pressure corresponding to the portion of the water head difference by the height H. In this manner, the nozzle is kept in a state of being filled with ink with the formation of meniscus on the opening surface.
Ink is discharged from the nozzle by pushing out ink in the nozzle by driving energy generating means. After ink is discharged, ink is filled in the nozzle by means of capillary force. During a recording operation, ink discharges from the nozzle and ink filling to the nozzle are repeated, and ink is suck from the ink chamber 1205c from time to time by way of the supply tube 1206.
When ink is sucked from the ink chamber 1205c to the recording head 1201, the position of the liquid surface of ink in the ink chamber 1205c is made lower than the lower end of the air induction needle 1205b. Then, the air outside is induced into the main tank 1204 through the air induction needle 1205b. Along with this, ink in the main tank 1204 is supplied to the ink chamber 1205c. Then, the lower end of the air induction needle 1205b is again immersed in ink in the ink chamber 1205c. While this action is repeated, ink in the main tank 1204 is supplied to the recording head 1201 along with the ink discharge from the recording head 1201.
Now, however, in the sub-tank portion 1201b of the recording head 1201, the air that enters after permeating resin material of the supply tube 1206 or the like, and the air dissolved to reside in ink are gradually accumulated. In order to exhaust excessive air accumulated in the sub-tank portion 1201b, the exhaust tube 1211, which is connected with an exhaust pump 1211a, is connected to the sub-tank portion 1201b. Here, a valve 1211b is provided for the exhaust tube 1211 for keeping the inside of the recording head 1201 in an appropriate negative pressure as described above. The valve 1211b is open only at the time of air-exhaust operation so as not to allow the inside of the recording head 1201 to present the atmospheric pressure.
In this respect, if overly viscous ink or the like is clogged in the ink discharge portion 1201g or bubbles are generated in the ink discharge portion 1201g by the accumulation of dissolved air in ink, these should be removed, and for that matter, a recovery unit 1207 is generally provided for an ink jet recording apparatus. The recovery unit 1207 is provided with a cap 1207a to cap the nozzle-opening surface of the recording head 1201, and a suction pump 1207c connected to this cap 1207a. Then, the suction pump 1207c is driven in a state where the nozzle-opening surface is capped by the cap 1207a to forcefully suck ink from the inside the recording head 1201 for the removal of the overly viscous ink or the like and excessive bubbles from the ink discharge portion 1201g. 
When the operation of recovery suction is performed, overly viscous ink or the like and excessive bubbles can be removed more effectively if the ink flow is faster. Therefore, to make the ink flow faster in the flow path 1201f, the sectional area of the flow path 1201f is made smaller. On the other hand, the sectional area of the filter 1201c is made as large as possible. As a result, the sectional area of the flow path 1201f is configured to be narrower below the filter 1201c. 
As has been given above, the description of the conventional ink supply system is made exemplifying the tube supply method. However, for the head integrated method or the pit-in method, the structure of the recording head on the downstream side of the filter is fundamentally the same as that of the tube supply method, although the structure of the supply passage from the ink tank to the recording head is only different from each other.
The recording head described above forms an airtight space with a flow path cover, which is bonded to the liquid chamber portion of the sub-tank unit. However, if such airtightly closed condition of each chamber is not perfect, leakage may take place. For example, some bubbling is embraced in the bonding portion at the time of coating bonding agent, and such bubbling is inclusively contained when the tank unit and the flow path cover are bonded, thus creating a hollow portion that connects liquid chambers. Then, leakage takes place through such hollow portion.
If the tank unit and flow path cover are bonded after coating bonding agent in a state where bubbling is inclusively contained as shown in FIG. 17A, a hollow 1500 that connects liquid chambers A and B as shown in FIG. 17B. As a result, leakage takes place between the liquid chambers A and B, and due to such leakage, ink in each of the liquid chambers is mixed. Thus, there is a possibility that color mixture occurs.
Also, when hardening cure is given to bonding agent, for example, vapor generated from the tank unit and the flow path cover is developed as the temperature rises. Then, a hollow that connects the liquid chambers is created, and leakage takes place through the hollow thus created. Here, in FIG. 17A, a reference numeral 1371 designates bonding agent, and 1372, mixed bubble.
Now, when bonding agent is cured after bonding the tank unit and the flow path cover together as shown in FIG. 18A, vapor is generated from material of the members constituting the tank unit and the flow path cover as shown in FIG. 18B. With the development of vapor mixed in bonding agent, the hollow that connects liquid chambers is created as shown in FIG. 18C, and leakage takes place between the liquid chambers A and B. Then, as in the case described above, ink is mixed with each other due to such leakage, and there is a possibility that color mixture occurs. Here, in FIG. 18B, a reference numeral 1373 designates bubbles.
The present invention is designed with a view to solving the problems discussed above. It is an object of the invention to materialize the provision of an ink jet recording head capable of preventing bubbles from being inclusively retained in bonding agent when the covering member is bonded to the liquid chamber portion of the recording head, thus eliminating the drawback that may be caused by leakage between liquid chambers, as well as to materialize the provision of an ink jet recording apparatus using such recording head. It is also an object of the invention to provide a method for manufacturing such ink jet recording head.
In order to achieve the object described above, the ink jet recording head of the present invention comprises an ink tank; a nozzle for discharging ink; a liquid chamber for retaining a specific amount of ink supplied from the ink tank through a filter, while supplying ink to the nozzle; and a covering member to be bonded to the liquid chamber, and on the circumference of the liquid chamber a groove is formed to enable bonding agent to be coated therefor, and on the circumference of the covering member, an extrusion is formed to be fitted into the groove. For this ink jet recording head, gas releasing means is provided for releasing gas remaining in the bonding agent to the outside of the groove when the covering member is bonded to the liquid chamber by fitting the extrusion into the groove after the bonding agent is coated in the groove.
In accordance with the ink jet recording head of the present invention, gas remaining in bonding agent is released to the outside of the groove. As a result, no void is formed by gas remaining in the bonding agent, which may otherwise connect liquid chambers adjacent to each other, thus airtightly close each of the liquid chambers, hence making it possible to prevent leakage from occurring between liquid chambers.
Further, the structure may be arranged to provide the gas releasing means on the covering member side. In this case, the gas releasing means may be formed as a hole that penetrates the surface of the covering member to the backside thereof along the extrusion of the covering member. With the structure thus arranged, gas remaining in the bonding agent is released outside the groove through the hole of the covering member when the covering member is bonded to the liquid chamber by fitting the extrusion into the groove.
Or it may be possible to structure the gas releasing means to be on the liquid chamber side. In this case, the gas releasing means is a passage communicating the space in the groove and the space in the liquid chamber. With this structure, gas remaining in the bonding agent is released from the groove to the liquid chamber through such passage when the covering member is bonded to the liquid chamber by fitting the extrusion into the groove.
Also, the structure may be arranged to provide a set of the ink tank, nozzle, and liquid chamber in plural numbers individually.
Further, the structure may be arranged to configure each of the liquid chambers radially so as to expand from the plural nozzles toward the ink tanks to make the width formed by the plural nozzles smaller than the width formed by the plural ink tanks.
Also, the groove may be structured so that the width thereof expands gradually from the bottom face to the entrance thereof, and the sectional shape is formed with a smoothly curved line connecting the bottom face and the side face. In this manner, the width of the groove is made larger form the bottom face thereof toward the entrance gradually, thus making it easier to coat bonding agent, and also, the bonding agent is applied deep into the bottom portion reliably, hence eliminating such drawback that the bonding agent has bubbles inclusively. Also, bubbles tend to stay at the corners, but with the smoothly curved line formed for the groove to connect the bottom face and side face thereof, it becomes possible to prevent bubbles from staying at corner portions.
Further, the aforesaid extrusion has the sectional shape having rounded tip portion. As compared with the one having the square tip, it is in contact with bonding agent smoothly to press it gradually when it is pushed into the bonding agent in the groove. As a result, it becomes possible to prevent more reliably bubbles from being generated in the bonding agent or to allow them to be contained in it inclusively.
Also, the structure may be arranged to enable the height of the extrusion of the covering member and the amount of bending of the covering member as a whole to be in relations of the height of extrusion greater than the amount of bending of covering member as a whole. With the structure thus arranged, even if the central portion of the flow path cover is caused to float up by the amount of bending as a whole, the tip of the extrusion on the central portion of the flow path cover enters the groove. Therefore, it is made possible to prevent leakage or the like from being generated between liquid chambers themselves due to defective bonding or the like.
Also, the structure may be arranged so that the shape of the groove observed from the side having the covering member bonded is formed by a vertically directional component, a horizontally directional component, and a diagonally directional component intersecting at least either one of the vertically directional component and the horizontally direction component. In this way, even if there exists xe2x80x9cplayxe2x80x9d between the groove and the extrusion, the groove formed by such three directional components suppresses such xe2x80x9cplayxe2x80x9d as much as possible to make it possible to bond them in a better precision.
Further, the structure may be arranged so that the bonding agent coating (application) area of the portion having arbitrary four intersecting components or more is larger than the bonding agent coating area of the portion having arbitrary three components or less among those components of the groove. Since bubbles are easier to be generated on the intersecting portions in particular when bonding agent is coated. However, on the portion where the bonding agent coating area is made larger as described above, the coating amount of the bonding agent is larger than the other portions. Therefore, even if bubbles are slightly generated, the influence exerted by such bubbles becomes relatively small, and the possibility is smaller that voids are formed between liquid chambers by leakage or the like due to the existence of such bubbles.
Also, the ink jet recording apparatus of the present invention uses the ink jet recording head of the present invention as described above.
Also, the method of the present invention for manufacturing an ink jet recording head, which is provided with an ink tank, a nozzle for discharging ink, a liquid chamber for retaining a specific amount of ink supplied from the ink tank through a filter, and a covering member to be bonded to the liquid chamber, and on the circumference of the liquid chamber, a groove being formed for bonding agent to be coated therein, and on the circumference of the covering member, an extrusion being formed to be fitted into the groove, comprises the steps of coating the bonding agent in the groove; bonding the covering member to the liquid chamber by fitting the extrusion into the groove; and releasing gas remaining in the bonding agent to the outside of the groove.
In accordance with the aforesaid method of the present invention for manufacturing an ink jet recording head, gas remaining in the bonding agent is released outside the groove. Therefore, the voids that may connect the liquid chambers adjacent to each other are not formed by gas remaining in the bonding agent, hence airtightly closing each of the liquid chambers reliably. Then, it becomes possible to manufacture an ink jet recording apparatus capable of preventing leakage from being generated between liquid chambers.
Further, the structure may be arranged so that a hole is provided for the covering member penetrating the surface of the covering member to the backside thereof along the extrusion, and the aforesaid step of releasing gas remaining in the bonding agent to the outside of the groove comprises the step of releasing the gas to the outside of the groove through the hole.
Or the structure may be arranged so that a passage is provided for the liquid chamber communicating the space in the groove and the space in the liquid chamber, and the step of releasing gas remaining in the bonding agent to the outside of the groove comprises the step of releasing the gas to the outside of the groove through the passage.
Also, the step of coating the bonding agent in the groove is to continuously coating the bonding agent during the period from the start to the end of coating the bonding agent. With the structure thus arranged, it is made possible to suppress the mixture of bubbles in the bonding agent being coated.
Further, the structure may be arranged so that the traveling speed of the needle with respect to the groove is changed when coating the bonding agent on the straight portion of the groove and at the corner portion of the groove, while constantly keeping the coating amount of the bonding agent discharged from the needle per unit time. If coating is carried out at the same speed for all the portions of the groove, the coating amount of bonding agent becomes larger at the corner portions of the groove than the straight portions thereof. Therefore, the traveling speed of the needle increases at the corner portions and decreases on the straight portions. In this manner, it becomes possible to stabilize the coating amount, while implementing the prevention of bubble inclusion in bonding agent.
Or the structure may be arranged so that the discharge pressure of the bonding agent from the needle is changed when coating the bonding agent on the straight portion of the groove and at the corner portion of the grove, while constantly keeping the traveling speed of the needle for discharging bonding agent with respect to the groove. In this way, as in the structure described above, it becomes possible to stabilize the coating amount, while implementing the prevention of bubble inclusion in bonding agent.
Also, the structure may be arranged so that the method of manufacture further comprises a step of curing the bonding agent to be hardened after the step of releasing gas remaining in the bonding agent to the outside of the groove.
Further, the structure may be arranged so that the aforesaid curing step comprises a pre-curing step for hardening the bonding agent at a comparatively low temperature, and a regular curing step for hardening the bonding agent at a comparatively high temperature. The portions of the bonding agent, which are in contact with the groove and the flow path cover are half hardened through the pre-curing. Therefore, even if vapors are generated from the structural material of the groove and the flow path cover when the regular curing is carried out at high temperature, such vapors cannot penetrate the half-hardened bonding agent, hence making it possible to suppress the mixture of vapors in the bonding agent.